The present invention relates to friction clutches in general, and more particularly to improvements in friction clutches which can be utilized in automotive vehicles, for example, to transmit torque from a flywheel or an analogous driving member which is rotated by the engine to the rotary input shaft of the transmission or an analogous driven member. Still more particularly, the invention relates to improvements in friction clutches of the type wherein at least one clutch plate is movable axially of but cannot perform angular movements with respect to a rotary component, such as the aforementioned input shaft.
It is already known to provide a friction clutch for automotive vehicles with a clutch plate having a disc-shaped intermediate pressure plate flanked by two friction discs which are movable toward and away from each other, i.e., toward or away from the respective sides of the intermediate pressure plate. The first friction disc is disposed between the flywheel and the intermediate pressure plate, the second friction disc is disposed between the intermediate pressure plate and a main pressure plate, and the latter can be biased by a clutch spring so that, when the clutch is engaged, the main pressure plate urges the second friction disc against the intermediate pressure plate which, in turn, urges the first friction disc against the rotating flywheel or an analogous driving member. The clutch spring is normally a Belleville spring which is installed between two seats, one on the cover of the clutch and the other on the main pressure plate. Reference may be had to German Offenlegungsschrift No. 2,048,957 which discloses a friction clutch of the just outlined conventional design. The clutch serves to transmit torque to a shaft or another driven member which is provided with a hub having a radially outwardly extending flange. The flange is flanked by two motion transmitting discs which are fixedly connected to each other by rivets. The motion transmitting discs are further connected to and share the angular movements of the hub. Resilient means are interposed between the motion transmitting discs and the hub. The radially outermost portions of the motion transmitting discs carry friction discs one of which is fixedly riveted to the respective motion transmitting disc. The other friction disc is coupled to the respective motion transmitting disc by claw-shaped projections which extend into complementary recesses or sockets of the associated motion transmitting disc. The coupling including the just mentioned claws and sockets is such that the other friction disc has some freedom of axial movement with reference to but cannot move radially of the one friction disc. More specifically, both friction discs can move axially of but are held against any radial movement relative to the hub of the shaft.
The friction discs of the friction clutch which is disclosed in the aforementioned German publication flank an intermediate pressure plate and are disposed between a rotary flywheel and a main pressure plate. The latter can be urged against the adjacent friction disc by the clutch spring in response to termination of application of the clutch-disengaging force whereby the thus engaged friction disc bears against the intermediate pressure plate which urges the other friction disc against the flywheel. The two pressure plates include radially outwardly extending portions which project into suitably configurated recesses of the cover and are attached to the cover for angular movement therewith. The connections between the two pressure plates and the cover are such that the pressure plates are held against radial movement. The cover shares all angular movements of the flywheel.
The just described conventional friction clutch exhibits certain structural as well as functional drawbacks. Thus, the coupling including the claws in the other friction disc and the sockets in the associated motion transmitting disc is rather sensitive, the same as the connections between the two pressure plates and the cover. A certain play is invariably necessary in order to allow for assembly of the coupling and connections during assembly of the friction clutch. The play cannot be held to a highly desirable minimum for several reasons, such as extremely high cost of accurate machining and/or unavoidable tolerances irrespective of the accuracy of machining and/or other shaping operations. The play increases when the friction clutch is in use as a result of progressing wear upon the male and female component parts of the aforementioned coupling and connections when the clutch is in use. This, in turn, results in the generation of readily detectable noise. Another drawback of the just described conventional friction clutch is that it is not readily possible to ensure that each and every claw or an otherwise configurated male coupling or connecting member engages the respective female coupling or connecting member, i.e., the wear upon certain coupling or connecting members is more pronounced than that upon the other coupling or connecting members so that, even after relatively short periods of use, the extent of axial movement of friction discs relative to each other and/or the extent of movement of the two pressure plates relative to the cover deviates from an optimum value. Consequently, when the clutch is supposed to be disengaged, its component parts continue to transmit torque from the flywheel to the shaft with the result that the transmission cannot be shifted into a different gear. Moreover, even short intervals of idleness of the friction clutch can lead to deposition of rust on the complementary surfaces of the male and female components of the aforementioned coupling between the two friction discs as well as the connections between the two pressure plates and the cover. This phenomenon is known as fitting corrosion. Also, dust which develops as a result of wear upon the friction linings is likely to deposit on the complementary surfaces of the male and female coupling and/or connecting members after a relatively short period of use of the clutch. The dust is mixed with oil and moisture to form a viscous mass which causes the neighboring parts of the clutch to adhere to each other, especially under the action of heat which is generated in response to repeated engagement and disengagement of the clutch. It has been found that the just discussed viscous mass is likely to permanently bond certain parts of the clutch to the neighboring parts. This exerts adverse influence upon axial movability of the parts, i.e., certain parts (including the friction discs and the pressure plates) are either incapable of performing requisite axial movements or are held against any axial movement with the result that the clutch cannot perform its torque transmitting function or is altogether incapable of interrupting the transmission of torque when the need for such interruption arises.